Figure 4

Transglutaminase 2b Is Enriched in Epi1 and Functions to Maintain the Integrity of the Epicardial Cell Layer

(A) Expression of tgm2b. Color key indicates range of log₂ transformed FPKM values.

(B) mRNA staining of tgm2b (magenta), tcf21 (cyan), and tbx18 (orange) in a 5 dpf heart. (B′ and B″) A nucleus (asterisk) in the epicardial region surrounded by tgm2b, tcf21, and tbx18.

(C) The epicardium in a 5 dpf control larva.

(D) Disrupted epicardial integrity in a 5 dpf KO tgm2b larva.

(E) Absolute quantification of tcf21:H2B-Dendra2⁺ epicardial cell numbers at 5 dpf in transient tgm2b knockouts (Control, KO tgm2b) and stable tgm2b mutants (heterozygous, tgm2b^wt/mut; homozygous, tgm2b^mut/mut). Larvae from two mutant lines were analyzed.

(F) Absolute quantification of tbx18:myr-Citrine⁺ epicardial cell numbers at 5 dpf.

(G) The epicardium in a 66 hpf control embryo. White arrows indicate epicardial cells, and red arrowheads indicate cells in the PEO.

(H) Reduced epicardial cell numbers in a 66 hpf KO tgm2b embryo.

(I and J) Absolute quantification of tcf21:H2B-Dendra2⁺ epicardial (I) and proepicardial (J) cell numbers at 66 hpf.

(K) Proliferation in the epicardium of a 77 hpf control larva (white arrows).

(L) Increased epicardial proliferation in a KO tgm2b larva.

(M) Relative quantification of proliferating epicardial cells.

(N) Absolute quantification of tcf21:H2B-Dendra2⁺ epicardial cells. Scale bars: 50 μm in (C), (D), (G), and (H); 20 μm in (B); 10 μm in (K) and (L); and 5 μm in (B′) and (B″). Color channels were adjusted separately for brightness and contrast. (C), (D), (G), and (H) are projections; (B), (K), and (L) are single optical sections. Data are represented as median, first, and third quartiles (box). Significance was calculated using Welch’s t test. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001. V, ventricle; Ab, antibody.

See also Figure S6.